A fiber optic node may have a broadband optical receiver, which converts the downstream optically modulated signal coming from the headend/hub to an electrical signal going to the homes. Presently, the downstream signal is a RF modulated signal that typically begins at 50 MHz and ranges from 550-1000 MHz on the upper end. The fiber optic node also contains a reverse/return path transmitter that sends communication from the home back to the headend. In North America, this reverse signal is a modulated RF ranging from 5-40 MHz while in other parts of the world, the range is 5-65 MHz.
In a typical non-scalable node, the return path may be regulated by a diplex filter with the low (return) frequency side set to pass approximately 5-40 MHz and the high (forward) side set to pass approximately 51-1000 MHz. As stated above, other frequency splits may be used such as the European split of approximately 5-65 MHz reverse and approximately 85-1000 MHz forward. The present state of the art requires that the diplex filters be physically changed in order to change the frequency split and to allow more low or return bandwidth. In an amplifier the presence of both forward and return provides a circular feedback path and diplex filters, with high isolation at the crossover frequency are required to prevent oscillation. In a node there is no circular path as the input is light and output is RF and oscillations are not a problem.
A typical CATV R-ONU generally has a return path that is non-adjustable without physically changing the diplex filters. Referring to FIG. 1, a block diagram of a typical CATV R-ONU 10 is shown. In the CATV R-ONU 10, the fiber optic input signal may be converted to an RF signal and then combined on the output with the incoming return signal by the use of a diplex filter 12. The typical output signal level may be approximately 16-20 dBmv while the return level may be approximately 40-50 dBmv. The bandwidth of the return is generally limited to 40 MHz by the diplex filter 12 and the frequency between 40 and 51 MHz is generally unusable.
A typical CATV Node has a return path that is non-scalable without physically changing the diplex filters. Referring to FIG. 2, a block diagram of a typical CATV Node 20 is shown. In the CATV node 20, the fiber optic input signal may be converted to an RF signal and then combined on the output with the incoming return signal by the use of a diplex filter 22. The typical output signal level may be approximately 38-52 dBmv, while the return level may be approximately 15-20 dBmv. The bandwidth of the return is generally limited to 40 MHz by the diplex filter 22 and the crossover frequency between 40 and 51 MHz is generally unusable.
In the past, different attempts were made to try and overcome the above issues. As may be seen in FIGS. 3 and 4, attempts to use a directional coupler or a 2-way splitter both with and without phase cancellation were tired, but it proved to be problematic and was not pursued.
Therefore, it would be desirable to provide a device and method that overcomes all of the above issues.